Regulating device for a timepiece

ABSTRACT

A regulating device employing two balance springs, preferably exerting the same couple, which are drawn from alloys having approximately the same thermal compensation. The two balance springs can either be coiled in the same direction or in opposite directions. The adjustments of the balance springs being such that, during their movements of expansion and contraction, their centers of gravity shift in diverging directions so as to compensate, at least partially, for the radial pressures exerted on the balance shaft.

United States Patent l l i 1' 1 Inventors Pierre Beguin;

Pierre-Andre Beguin, both oi Le Locle, Switzerland Appl. No. 879,129

Filed Nov. 24, 1969 Patented Aug. 17, 1971 Assignee Portescap Le Porte, Eehappement Universal S. A. Ll Chlux De Fonds, Switzerland Priority Nov. 29, 1968 Switzerland 17.874/68 REGULATING DEVICE FOR A TIMEPIECE 7 Claims, 4 Drawing Figs.

11.8. CI,..- 58/109, 58/28 H Int. Cl G04b 17/14 Field of Search 58/109,

llO,28 B, lO8, H4, 107

[56] References Cited UNITED STATES PATENTS 3,084,316 4/1963 Zemla 58/28 3,186,157 6/1965 Fauret etal 58/28 FOREIGN PATENTS 132,567 7/1951 Sweden 58/107 45,160 5/1909 Switzerland 58/107 Primary Examiner- Richard B. Wilkinson Assistant Examiner-Stanley A. Wal Anomeys- Kenwood Ross and Chester E. Flavin ABSTRACT: A regulating device employing two balance springs, preferably exerting the same couple, which are drawn from alloys having approximately the same thermal compensation. The two balance springs can either be coiled in the same direction or in opposite directions. The adjustments of the balance springs being such that, during their movements of expansion and contraction, their centers of gravity shift in diverging directions so as to compensate, at least partially, for the radial pressures exerted on the balance shaft.

TIT vt iii 5:. i

PATENTED AUG! 7 I 3, 599 .423

SHEET 1 [IF 2 FIG. 2

I N V ENTORS I Herr: BEGU/N Pierre A pa're' BEG U/N BY Wanna? @014 @bAZbz7Za4/6 n REGULATING DEVICE FOR A TIMEPIECE The present invention comprises regulating device for a timepiece in the form of a balance wheel subject to the action of at least two balance springs which may serve various purposes, more especially, in the case of electric timepieces, the purpose of making possible the use of balance springs as conductors of power.

The aim of the present invention is, by the use of at least two balance springs, to improve the qualities of the regulating member, principally as regards its thermal compensation, that is to say, its insensitiveness to variations in temperature, and, to a' lesser degree, as regards its isochronism, that is to say, its insensitiveness to variations of amplitude.

The drawing shows, by way of example, one embodiment of the object of the invention, and one modification thereof.

FIG. 1 is a diagram showing the dispersion of the thermal coefficients of balance springs drawn from two different alloy casts.

FIG. 2 is a plan view of a first embodiment device for a timepiece.

FIG. 3 is a cross-sectional view along line III-III in FIG. 2, and

FIG. 4 is a plan view of a detail of a modification.

As regards thermal compensation, the invention is based on the fact that, upon the casting of an alloy for balance springs for timepieces, the mean thermal coefficient of the balance springs obtained by means of the alloy seldom falls, between two determined temperatures, on the zero value desired.

This phenomenon is due to the fact that even very slight variations in the composition of the alloy have considerable effects on the thermal coefficient of the completed balance spring.

The fact that the homogeneity of the alloy cannot be perfect gives rise to a dispersion of the thermal coefficient of the balance springs that are drawn from one single alloy cast which, shown graphically, is embodied in a curve of bell-jar pattern, a so-called "gaussian curve", as is shown in the diagram in FIG. 1. i

In the diagram, the number N of parts involved is entered on the y-axis, while the thermal coefiicient CT, indicated in seconds per degree Centigrade, is entered along the x-axis. The curves 1 and 2 embody the thermal coefficients of balance springs drawn from two alloy casts, of which one has a mean value of l.0 sec/ C., with a dispersion lying between 1 .5 and -0.5, while the other one is symmetrical with respect to the y-axis, with +1.0 as the mean, for a dispersion lying between +0.5 and +1.5.

From these two curves, it will be seen that, in pairing up balance springs whose respective thermal coefficients are equal but of opposite signs, a new curve is obtained, shown at 3, corresponding to a thermal coefficient with a mean value of zero and with a zone of dispersion lying between O.5 and +0.5 sec/ C.

Hence, therefore, the use of two balance springs with coefficients that are equal thermally but of opposite signs makes it possible to achieve a very high degree of thermal compensatron.

As regards the ranges of temperatures within which thermal compensation has to be provided, it should be noted that these ranges vary according to the intended purpose of the timekeeping unit. They generally amount to at least 30 C., between the extreme values of -50 C. and +100 C., for example from 50 to C., from 25 to +25 C., from +4 to +36 C., and from to +50 C.

Another considerable advantage of the present invention resides in the fact that the pairing springs, the thermal coefiicients of which are equal but of opposite signs make it possible to make use of alloy casts which, but for that, would be of a regulating As regards isochronism in the regulating'device, the arrangement described has the advantage that, by arranging the balance springs in such a way that their center of gravity is shifted in two opposite directions in the course of their movements of expansion and contraction, in practice the radial pressures exerted by the balance springs on the balance shaft compensate each other. In other words, in practice, without using terminal curves, conditions are achieved which, but for that, would not be obtained except by means of balance springs of the Breguet type, which are considerably more expensive.

The first embodiment of the regulating device shown in FIGS. 2 and 3 comprises a balance 4 whose shaft 5 is pivoted between the plate of a clockwork movement, designated by 6, and its balance-cock, designated by 7. This latter carries a cock endstone 8 on which is mounted a movablestud-holder 9 itself carrying, mounted thereon in such a way as to be able to turn without driving the stud-holder around the regulator, designated by 10.

The shaft 5 of the balance carries two collets 11 and 12 to which are fastened two balance springs de'signatedby l3 and 14 respectively.

One of the springs, balance spring 13, is secured at its outer end to a stud 15 carried by the balance-cock 7, while the other spring, balance spring 14, is secured to a stud 16 carried by a lug 9a of the stud-holder 9.

The curb pin and balance-spring boot, designated by 17 and 18, respectively, and carried by a lug 10a of the index 10, act on the balance spring 14.

As regards isochronism, it should be noted that the balancing out of the radial pressures exerted on the shaft 5 by the balance springs is achieved, in the example shown, by using two balance springs coiled in the same direction, their outer pinning-points, that is studs 15 and 16, being at a relatively great distance from each other; it would be possible to consider the case in which the said studs would be diametrically opposite with respect to the center of the balance wheel. Further, though this condition is not absolutely obligatory, the inner pinning-points for the balance springs, designated by 19 and 20 respectively, are diametrically opposite.

In this arrangement, the development of the two balance springs is always symmetrical, this feature bringing with it the maintaining of the'center of gravity of them coinciding with the axis of the shaft 5.

A similar effect can be obtained with shown in FIG. 4, in which the two balance springs, designated by 21 and 22, respectively, are coiled in opposite directions, their outer pinning-points, that is studs 23 and 24, respectively, being located very close to each other, and their inner pinning-points coinciding with each other, when seen in a plan view, as is indicated by the arrow 25; it is also possible to consider the case in which the studs 23 and 24 would be situated on one and the same radius with respect to the center of the balance wheel. In reality, since one of the balance springs, in the present instance that designated by 21, has its active length limited by the curb pin and boot l7 and 18, the exact point of the balance spring 21 which should be located op posite the stud 24 is situated between the boot l8 and the stud 23, substantially as shown in the drawing.

Due to this arrangement, when one of the balance springs contracts, the other one expands, and vice versa. ln this arrangement, the radial pressures exerted by the balance springs on the shaft 5 are only partially compensated for, due to the fact that the center of gravity shifts further from the axis of the shaft 5 during expansion than it does during contraction, the value of the radial pressure increasing with the distance between the center of gravity of the balance spring and the axis of the balance wheel.

It should be noted that, in the case of the first embodiment, as in that of the modification too, the balance springs cannot the arrangement residual radial pre erit-{is "seen-taste be located in one and the same plane, so that it follows that a' till acting .5 unit or grilles fill" aw lowest, the closer to each other the balance springs areplaced and the greater the distance between the bearings for the shaft.

ble, if practical reasons impose that solution.

It should be noted that the conformation of the balance wheel does not play any role. It may be formed from a single or from several wheels, or from bars; it could be asymmetrical or could carry one or more mechanical or electromechanical organs, such as screws, inertia blocks, coils or magnets being parts of a transducer device. v The inner end of the balance springs could be secured to the balance shaft by any conventional means, such as by collet means, as in the examples described and shown here, or also by adhesive techniques, by riveting, by brazing or by other means, while the outer end of the balance springs could be secured to the frame by means of studs, as in the examples shown here, or without the intervention of these latter, by pinning, by pinching, by adhesive means, by brazing, by riveting or by other means.

It should be noted that, by securing at least one of the balance springs to a movable part, such as the stud-holder 9 of the first embodiment, it is possible to put the clockwork into beat, that is to say to adjust the position of the dead-point with respect to the escapement device. Once this position has been obtained, the result is not necessarily that the balance springs are without tension but, rather; that their respective amounts of winding balance each other out.

As regards the index-assembly, the fact that it acts on only one of the balance springs makes possible slight adjustments to the daily rate which are more accurate than in the case in which the regulating member includes only a single balance spring.

Finally, itshould be noted that the present arrangement is particularly indicated in its application to high frequencies oscillations, for example higher than 21,600 vibrations an hour, with the ability to rise to 360,000 and even higher.

In fact, the more the frequency is raised for a given balance wheel, the larger the cross section of the balance spring should be for a given length, since the duration of the period is inversely proportional to the square root of the couple. In the case of a frequency being doubled, for example, where the period T'=T/2, theory gives:

where I the moment of inertia of the balance wheel,

c= couple of the balance spring corresponding to the period T.

It will be seen that, for doubling the frequency, it is necessary to quadruple the couple of the balance spring, which is the equivalent of mounting on a single balance wheel four balance springs identical with the first one. The duration of the period being also proportional to the square root of the moment of inertia of the balance wheel, it will be sufficient, in the example of a doubled frequency and starting from a given regulating organ, to adopt a moment of inertia of the balance wheel that is reduced by a half, and to use two balance springs identical with the first one. The dimension of the said balance springs thus remain within the usual norms of watch-making, something that is not always the case when only a single balance spring is being used.

To this respect, the present invention makes it possible to safeguard one important property of balance springs, that is keeping them of an adequate length. In fact, it is well known that, the shorter is a balance spring, the more it absorbs energy when is rnak ing a balance wheel oscillate in given conditions of am litp e areas-m f enemy. tear.

E5 9 fihl fitynnytasidit analtab p on; cialtop hetef ieiensy.andsthesaecu iy of 75 the timepiece. It appears that, the more the frequency is increased, the more the balance spring must be shortened with respect to its cross section. This modification of its proportions may spoil its regulating qualities. The employment of at least two balance springs for obtaining a high frequency makes it possible to avoid this danger.

The increase in frequency also has the following consequence:

The thermal coefficient of a timepiece equipped with a regulating device consisting of a balance wheel and a balance spring is the result of the thermal coefficients of these two ele- 1 ments, as well as of the influence'of temperature on the oils, on the operations of the escapement, on the frictions, etc. When the temperature increases, the expansion of a monometallic balance wheel produces an increase in its moment of inertia which would produce a certain lower losing rate if other influences did not exist. Under the same conditions, a noncompensating balance spring produces a losing rate some ten times greater. The role of the compensating balance spring is particularly to neutralize the sum of these two losing rates. Now, the perfect compensation for a given balance wheel and balance spring exists only at a determined frequency, because the effect of the balance with respect to that of the balance spring decreases when the frequency increases. The result is that a single balance spring connected successively to balance wheels with decreasing moments of inertia, for obtaining increasing frequencies, yields thermal coefficients tending towards a gain in the presence of heat. The influence on the thermal coefficient is a gain of a fraction of a second a day for each degree Centigrade when applied to an increase of the frequency from 18,000 to 36,000 vibrations an hour.

This effect is of minor importance for current accuracy, but is not negligible when a higher degree of accuracy is being sought for.

In the case of the present regulating device, this phenomenon may be taken into account when the balance springs are paired, this being carried out by selecting their thermal coefficient in such a way that their mean tends also to compensate for effects due to the balance wheel, to the oils, to the operation of the escapement and to other causes, as well.

Finally, it should be noted that the present regulating device may comprise more than two balance springs, the couples of which would not necessarily be equal, each playing its part, according to its possibilities, in compensating for the effects of one or other of the causes of inaccuracy.

What we claim is:

1. In a regulating device for a timepiece comprising:

a plate,

a balance cock,

a balance,

a balance shaft pivoted between the plate and balance cock,

a pair of balance springs formed from alloys having approximately the same thermal compensation and having coefficients equal thermally but of opposite signs for compensating each other,

the balance springs of the pair being arranged for the shifting of their centers of gravity in diverging directions during their movements of expansion and contraction for compensating for the radial pressures exerted on the balance shaft.

2. in the regulating device as claimed in claim 1, the means thermal coefficient of the balance springs compensates for the effects due to the balance and to the oils and to the escapement device operation.

3. in the regulating device as claimed in claim 1, the temperature range for optimum compensation being at least thirty degrees Centigrade and between the extreme temperatures of 50 and+l00 C.

4. In the regulating device as claimed in claim 1, the balance springs being coiled in opposite directions, their outer pinning poihtsabein'g loated st1bstaiiti'a'lly or? the same radius with respect to the axis of oscillation of the balancti wheel.

5. In the regulating device as claimed in claim 1, the balance springs being coiled in the same direction, their outer pinningpoints being substantially diametrically opposite with respect to the axis of oscillation of the balance wheel.

of the regulator-assembly. v

7. In the regulating device as claimed in claim 1, the frequency of the oscillations of the balance wheel being higher 6. In the regulating device as claimed in claim 1, the active 5 than 2l6O0 vibrations per hour' length of one of the balance springs being adjustable by means 

1. In a regulating device for a timEpiece comprising: a plate, a balance cock, a balance, a balance shaft pivoted between the plate and balance cock, a pair of balance springs formed from alloys having approximately the same thermal compensation and having coefficients equal thermally but of opposite signs for compensating each other, the balance springs of the pair being arranged for the shifting of their centers of gravity in diverging directions during their movements of expansion and contraction for compensating for the radial pressures exerted on the balance shaft.
 2. In the regulating device as claimed in claim 1, the means thermal coefficient of the balance springs compensates for the effects due to the balance and to the oils and to the escapement device operation.
 3. In the regulating device as claimed in claim 1, the temperature range for optimum compensation being at least thirty degrees Centigrade and between the extreme temperatures of -50* and +100* C.
 4. In the regulating device as claimed in claim 1, the balance springs being coiled in opposite directions, their outer pinning-points being located substantially on the same radius with respect to the axis of oscillation of the balance wheel.
 5. In the regulating device as claimed in claim 1, the balance springs being coiled in the same direction, their outer pinning-points being substantially diametrically opposite with respect to the axis of oscillation of the balance wheel.
 6. In the regulating device as claimed in claim 1, the active length of one of the balance springs being adjustable by means of the regulator-assembly.
 7. In the regulating device as claimed in claim 1, the frequency of the oscillations of the balance wheel being higher than 21,600 vibrations per hour. 